Process of recovering tar acids from crude tar



June 1, 1937. J. G. HATMAN PROCESS OF: RECOVERING TAR ACIDS FROM CRUDETAR- Filed July 20. use

NTQ FUGE m m N E H D.

SOLUTION PHENOLATE STORAGE TANK.

PUMP

INVENTOR. Juuus G HATNAN TAR ACID RECOVERY BY 7/M'M Q AWL ATTORNEY.

Patented June l, 1937 UNITED STATES PATENT OFFICE PROCESS OF RECOVERINGTAR- ACIDS FROM CRUDE TAR phia, Pa.

Application July 20,

Claims.

The present invention relates to the recovery of tar acids from cokeoven tar, and it consists in an improvement in the processes describedin the application of Charles M. Ambler, Jr. and Charles E. Underwood,Serial No. 754,718, filed November 26, 1934 and in the application ofthe present applicant, Serial No. 16,240, filed April 13, 1935.

In accordance with the usual practice of manufacturing coke, a quantityof tarry material results as a by-product. This tarry material, or crudetar as it will hereafter be called, ordinarily contains from 2 /2 to 6%of tar acids and a substantial quantity of water, which may amount to asmuch as 10% of the volume of the crude tar. The tar acids, which consistmainly of phenol and its homologues, such as the cresols and Xylenols,are valuable commercially, but are quite difficult to separate from thecrude tar in accordance with known procedures. ;The method of effectingsuch separation in accordance with prior art procedure has usually beento dehydrate the crude tar by evaporation or centrifugation andthereafter to distil this crude tar in such a manner as to separate theacid naphthalene fraction, boiling below 270 C. and commonly known astar oil, from the heavier tarry material, which is known as tar residue.Practically all of the tar acids contained in the crude tar boil withinthe tar oil range and are therefore distilled over with the tar oilfraction. The amount of tar oil distilled depends on the use to whichthe tar residue is put. These tar acids usually constitute between 10and of such fraction.

The separation of the tar acids from the tar oil fraction has ordinarilybeen accomplished by mixing this fraction with an aqueous caustic sodasolution in a concentration and proportion adapted to convert the taracids into their sodium salts. These compounds, which will hereafter bereferred to generally as phenolates, are readily dissolved in theresidual caustic soda solution and are separated from the tar oil afterthe neutralization treatment has been completed by allowing the mixtureto settle into an aqueous layer containing the phenolates and an oillayer con- .taining residual tar oil and then decanting. The aqueoussolution so obtained is thereafter treated with carbon dioxide gas oracidulated by means of sulphuric acid and the resulting tar acids areseparated from the sodium carbonate or sodium sulphate produced by thislast mentioned treatment by gravity settling.

In accordance with the abovementioned ap- 1935, Serial No. 32,315

plication filed by Ambler and Underwood, this prior art procedure issimplified by the extraction of the tar acids from the original tarrymaterial without subjection of this material to any preliminarydistillation. This is accomplished by mixing the crude tar directly witha basic solution such as an aqueous solution of caustic soda or causticpotash and thereafter separating the resulting phenolates from suchsolution promptly by means of centrifugal force.

While the procedure of the Ambler and Underwood application represents asubstantial im provem-ent over prior art processes, a certain amount ofdifficulty and expense is encountered in its practice because of thenecessity of acidulating relatively dilute phenolate solutions torecover tar acids therefrom. This difiiculty is overcome in connectionwith the procedure forming the subject matter oi application Serial No.16,240 described above, by returning a substantial proportion of thephenolate solution obtained during the early stages of the practice ofsuch a process to the mixing apparatus employed in the step of mixingthe crude tar with the alkali solution. By recycling the phenolatesolution in this manner the concentration of the phenolate solutionleaving the centrifuge may be substantially increased and the expense ofdistillation incident to the recovery of tar acids from the solutionresulting from treatment of this material may accordingly besubstantially reduced.

In the practice of a process of the character described in the abovementioned application, difficulty has sometimes been encountered in thecentrifugal separating step because of the formation of an emulsionwhich is diflicult to resolve into its constituents and the object ofthe present invention has been to avoid this emulsion difficulty.

The present invention relates to modifications in the process describedin the applicants prior case, in which the order and manner of addingthe aqueous phase materials to the crude tar is somewhat altered, inorder to obviate these diniculties. In accordance with the presentinvention, water and phenolate solution are added to the crude tar andare mildly mixed therewith prior to the addition of alkali solution tothe tar. While the physical basis for the improvement in separatingconditions attained by such a sequence of operations is not fullyunderstood, it has been found that a much more effective separation ofwater and phenolate solution from the crude tar can be accomplished bysuch a sequence of operations than by the operations described in theabove identified applications. A further feature of the inventionconsists in the discovery that the separate addition of water andphenolate solution to the crude tar prior to the mixing step results ina better separation of phenolates and water from the tar upon thesubsequent addition of alkali and centrifugation than can be obtained incases in which phenolate solution is recycled to the mixer as the oneaqueous phase and no water is separately added. A still further featureof the invention consists in the employment of a sequence of mixing andheating operations better adapted to effect separation of aqueous phasefrom tar than are the operations described in said applications.

The nature of the present invention can be best understood by referenceto the attached flow sheet. In practicing the invention, crude tar andwater are initially passed to a multistage mixing apparatus adapted tomildly mix these influents, and alkali solution which may be ofapproximately 8% concentration is introduced into this mixer at a laterstage of the operation in order that the crude tar may be somewhat mixedwith Water prior to the addition of such alkali. The mixing operation ispreferably performed at a temperature between 50 and 65 C. The materialleaving the mixer is then passed through a heater which is adapted toheat it to a temperature between '70 and 90 C. and is passed from thisheater to a continuous centrifugal separator where it is resolved intophenolate solution and residual tar. The phenolate solution is passed toa phenolate storage tank from which it may be Withdrawn from time totime for acidulation and distillation to recover tar acids therefrom.

During the early stages of the operation of a system of this character,the major proportion of phenolate solution passed to the storage tank isrecycled and returned directly to the inlet end of the mixer. Thisrecycling operation is continued until the aqueous eiiiuent from thecen-. trifuge reaches a concentration, for example,

' 15%, at which it may be economically treated for the recovery of taracids as discussed above. When the phenolate solution has reached thisdesired concentration, the proportion. of such solution returned to theinlet end of the mixer is diminished in order to effect such a balancebetween influent phenolate solution, alkali and water, as to produce asan aqueous effluent from this centrifuge a phenolate solution havingthis same desired degree of concentration.

A process of this general character is described in the above mentionedco-pending application of the present applicant. The present applicationrelates to three basic features of improvement over that application. Inaccordance with the first of these features the phenolate solutionrecycled to the mixer is introduced to the mixer at a point of saidmixer more remote from the heater than the point of introduction of thealkali. By operating the process in this manner the phenolate solutionis mixed with the crude tar to a mild extent before this crude tar iscontacted by alkali solution.

As pointed out in the above identified applications, it is desirablethat a substantial proportion of water be included among the materialsfed into the mixer. In order to attain this end, it is suggested in theapplicants prior case that water be added to the phenolate solutionprior to the re-introduction of this solution into the mixer.

A second basic feature of the present invention consists in thediscovery that emulsion difficulties are still further decreased by theseparate introduction of this added water and the phenolate solution.The applicant is unable to account for any reason why the separateaddition of water as such should avoid emulsion difficulties occurringwhen a small amountof water is added to further dilute the phenolatesolution and this diluted solution added to the tar, but experimentshave proven this to be the case.

To this end, the present invention involves the addition of water to apart of the mixer more remote from the heater than the point ofintroduction of the alkali solution simultaneously with there-introduction of the phenolate solution at a point which is likewisemore remote from the heater than the introduction of such alkali. Waterso added may be in the form of diluent for the phenolate solution inaccordance with the broadest aspects of the invention, but' thepreferred procedure in accordance with the invention involves separateintroduction of such Water and such phenolate solution. It has beenfound that the addition of a quantity of water amounting to at least 5%of the quantity of recycled phenolate solution at such a stage of theflow of materials through the system substantially aids in theattainment of the desired end. It will of course be understood that aquantity of water amounting to substantially more than this proportionbased upon the recycled phenolate solution is added during the earlystages of the operation of the system.

In accordance with the practice of the process of the invention afterthe initial stages of operation discussed above, therefore, recycledphenolate solution and water are simultaneously added to the inlet endof the mixer as illustrated, and alkali is continuously added at anintermediate point to the mixer, the proportion of water to phenolatesolution being gradually decreased as the concentration of the phenolatesolution is increased, until a proportion of water varying between 5 and15% based upon the quantity of recycled phenolate solution is added whenthe desired concentration of phenolate solution has been finallyattained.

The temperature conditions maintained in the practice of the processalso contribute very largely to the success thereof. It has been foundthat the mixing of the water, phenolate solution and alkali solutionwith the crude tar at a temperature between 50 and 65 C. contributes tothe separation, provided care is taken to avoid'tur- 'bulence of thematerial passing through the heater andconsequent further mixing andemulsification which might otherwise occur at these higher temperatures.This feature of the invention accordingly involves mixing of the tar and"aqueous phases at a reduced temperature and thereafter heating themixture so obtained under non-mixing conditions to a temperature bestadapted to facilitate centrifugal separation.

Modifications will be obvious to those skilled in the art and I do nottherefore wish to be limited except by the scope of the sub-joinedclaims.

I claim:

1. The process of separating tar acids from crude tar which comprisesadding a phenolate solution to said crude tar and mixing said solutionwith said tar, thereafter mixing an alkali solution with the mixture soformed and separating the resulting aqueous phase from the resulting tarphase by centrifugal force.

2. The process of separating tar acids from crude tar which comprisesadding a phenolate solution to said crude tar and mixing said solutionwith said tar at a temperature between and C., heating the resultingmixture to a temperature between and C. and separating the resultingaqueous phase from the resulting tar phase by centrifugal force.

3. The process of separating tar acids from crude tar which comprisesseparately adding a phenolate solution and Water to said crude tar andmixing said added materials with said tar, thereafter mixing an alkalisolution with the mixture so formed and separating the resulting aqueousphase from the resulting tar phase by centrifugal force.

4. The process of separating tar acids from crude tar which comprisesadding a phenolate solution to said crude tar and adding water to saidcrude tar in a proportion based upon the quantity of phenolate solutionadded amounting to at least 5% of said phenolate solution, mixing saidwater and said solution with said tar, thereafter mixing an alkalisolution with the mixture so formed and separating the resulting aqueousphase from the resulting tar phase by centrifugal force.

5. The process of separating tar acids from crude tar which comprisestreating said crude tar with an alkali solution to produce a phenolatesolution phase and a tar phase, separating the phenolate solution phasefrom the tar phase by centrifugal force, recycling the phenolatesolution phase into contact with further crude tar, adding water to saidcrude tar, mixing the recycled phenolate solution and the water withsaid crude tar, thereafter mixing an alkali solution with the mixture soformed between said phenolate solution, water and crude tar, andseparating the resulting aqueous phase from the resulting tar phase bycentrifugal force.

JULIUS G. I-IATMAN.

